a)
A bit about chains, steel:
http://lockitt.com/chaininfo.htmb)
Good chains:
http://www.abus.de/us/main.asp?ScreenLang=us&sid=297725857110613180720121099274152&select=0105b02&ArtikelGrID=151Some security tips:
1) Make sure bike is out of sight. When they don't notice it, they don't steal it. Worst garage with doors falling apart is often better than the best lock/chain/alarm. When going to park, especially from places where bikers hang out, make sure nobody follows you. They do sometimes follow bikes that look good, or are needed for parts.
2) Alarm and disk lock are for kids. Take a van, put the bike in and drive on. NOBODY will pay any attention most of the time. Alarm is useful for kids not climbing on your bike to make Facebook photos - NOTHING else.
3) Lock your bike with a good chain to a solid object, through frame (NOT just e.g. the front wheel).
4) Make sure the chain does not hang on the ground if possible at all. Ground makes a great lever. Make sure also that lock is in a hard to reach place. If it is awkward for you to lock it with a key, it will be hard to reach and pick the lock.
5) Never leave the bike in the same place for longer than one night if possible at all. When people see what they want and come well prepared, nothing can stop them. Busy, well lit streets are sometimes even less safe, because nobody will suspect and pay attention to a man in the crowd, picking something on his bike.
6) Chain AND lock are as good as the weakest link. I can only recommend Abus again, the 20 security factor by their standards. Don't know about other manufacturers that do it as good (I'm sure there are, just couldn't acquire, test, see...). Can it be hacked, cut? YES. Can it be done with small, easy to conceal tools, used 99% of the time by opportunistic thieves? NO, definitely not. Seen lots of Youtube videos of 1 meter cutters braking chains in no time. But they were 1 meter long levers, used against the ground (see point 4). That does not happen often.
Sources for all this mumbo-jumbo: local police, a retired locksmith who I've seen do wonders more than once and an experienced man from "the other side of the law".